The invention relates to a process for the cleaning of the sensor surfaces of a yarn monitoring system used in spinning machines to monitor the yarn and/or yarn quality. The sensor surface is the surface which utilizes an optical or capacitive monitoring process in order to ensure signal acquisition according to the principle of the monitoring system. The present device serves to carry out the process.
The sensor surface of a yarn monitoring system is subject to dirt accumulation from the spinning process. The capacity of the sensor surface to function in its role as yarn monitor must be ensured.
Non-Contact monitoring and scanning of the yarn is carried out separately for each spinning station. A yarn monitoring system is an important evaluation unit for the spinning machine. Optical or capacitive yarn monitoring as part of the yarn monitoring system supplies information on the presence of the yarn and/or on the yarn thickness or yarn quality. For this, the sensor surfaces must be placed in immediate proximity of the yarn.
It is characteristic for these optical or capacitive monitoring systems that the yarn monitoring system is provided with a yarn monitor with a U-shaped measuring gap. The running yarn is guided inside this measuring gap without contacting the structure of the monitor. In principle, the optical or capacitive yarn monitoring system is designed so that two sensor surfaces face each other in one and the same horizontal plane in the form of laterally delimiting surfaces within the measuring gap.
Considerable amounts of dust, dirt particles, and reviving particles are produced during the spinning process and tend to deposit on the sensor surfaces and consequently these sensor surfaces of the yarn monitoring system can quickly reach a state of dirt accumulation such as to distort measured values.
Since this condition of dirt accumulation varies in the different yarn monitoring systems of the spinning stations and since therefore no sure prediction about a critical state of dirt accumulation can be made, periodic preventive cleaning of the sensor surfaces must be carried out according to the present state of the art.
Yarn monitoring systems in a high price range are sometimes equipped with an evaluating unit which is able to indicate the development of a critical operational state via a second signal output, but nevertheless it remains necessary to clean the sensor surfaces of the yarn monitoring system.
A known method for cleaning the sensors is to blow out the measuring gap or to provide aimed blowing on the sensor surfaces installed there in order to remove the dirt or to blow constantly on the running yarn before it enters the measuring space in such manner that the freely movable fibers carried along by the yarn are imparted a change of direction and cannot be deposited on the optics or on the capacitor plates. However, with these devices an additional blowing device and its precise positioning is required. In addition, sticky reviving particles can often not be removed from the sensor surface. Blowing alone does not provide a sufficient cleaning effect.
Another cleaning possibility is of a mechanical nature. An existing practice is also for the operating personnel to carry out the cleaning of the measuring gap manually with a brush when a functional malfunction is signalled in a yarn monitoring system, i.e. that they mechanically clean the optical or capacitive sensor surfaces. The affected spinning station is stopped for this cleaning operation.
DE-OS 40-01-255 describes how the measuring space is always scraped off mechanically by means of a rotating profile brush made of an elastic material when no yarn is present (e.g. after yarn breakage). This rotating brush can be combined with a blowing and suction device and is installed in an automatic service carriage travelling alongside the work stations. On the whole this solution is very cost-intensive and requires for the cleaning process that no yarn movement be present. Cleaning is therefore tied to an undesirable event which the industry is always trying to prevent. The aging of the elastic material or a tilting of the profile brush can cause scratching of the optically active surface.